Ankle prosthesis

Abstract

A fixed-bearing ankle prosthesis may include tibial and talar components whose articulating surfaces directly contact one another. The tibial component defines medial and lateral concave condylar facets separated by a convex central portion. The talar component includes medial and lateral convex condyles separated by a concave central portion. The condyles each have a single radius of curvature in a medial-lateral plane such that each condyle has a circular-arc cross-section continuously extending from the respective medial or lateral edge of the talar component to the concave central portion. The medial-lateral radii of the condyles are smaller than corresponding radii of the condylar facets.

What is claimed is: 
     
       1. A fixed-bearing ankle prosthesis, comprising:
 a tibial component for attachment to a tibia, wherein the tibial component has first and second surfaces; and 
 a talar component for attachment to a talus, wherein the talar component has first and second surfaces and medial and lateral edges; 
 wherein: 
 at least a portion of the first surface of the tibial component is configured to be disposed adjacent the tibia; 
 at least a portion of the first surface of the talar component is configured to be disposed adjacent the talus; 
 at least a portion of the second surface of the tibial component and at least a portion of the second surface of the talar component contact one another directly to form an articulation interface between the tibial component and the talar component; 
 the articulation interface includes a bicondylar geometry such that the second surface of the tibial component defines a medial condylar facet and a lateral condylar facet and the second surface of the talar component comprises a medial condyle and a lateral condyle; 
 the medial and lateral condylar facets of the tibial component have concave circular arc cross-sections extending in a medial-lateral plane; 
 the medial and condyle of the talar component has a first single radius in the medial-lateral plane that defines a convex circular arc cross-section continuously extending, in the medial-lateral plane, from the medial edge of the talar component to a concave central portion of the talar component second surface separating the medial and lateral condyles; 
 the lateral condyle of the talar component has a second single radius in the medial-lateral plane that defines a convex circular arc cross-section continuously extending, in the medial-lateral plane, from the lateral edge of the talar component to the concave central portion of the talar component second surface; 
 the concave circular arc cross-section of the medial condylar facet of the tibial component has a radius in the medial-lateral plane larger than the first radius; and 
 the concave circular arc cross-section of the lateral condylar facet of the tibial component has a radius in the medial-lateral plane larger than the second radius. 
 
     
     
       2. The ankle prosthesis of  claim 1 , wherein the medial-lateral plane radii of the convex circular arc cross-sections of the talar component are between 92% and 96% of the corresponding radii of the concave circular arc cross-sections of the tibial component. 
     
     
       3. The ankle prosthesis of  claim 1 , wherein the medial and lateral condylar facets of the tibial component have concave circular arc cross-sections extending in an anterior-posterior direction, the medial and lateral condyles of the talar component have convex circular arc cross-sections extending in the anterior-poster direction, and anterior-posterior radii of the circular arc cross-sections of the tibial component are larger than corresponding radii of the circular arc cross-sections of the talar component. 
     
     
       4. The ankle prosthesis of  claim 3 , wherein the anterior-posterior radii of the circular arc cross-sections of the talar component are between 85% and 96% of the corresponding radii of the circular arc cross-sections of the tibial component. 
     
     
       5. The ankle prosthesis of  claim 1 , wherein a central portion of the tibial component second surface, which separates the medial and lateral condylar facets and which overlies the talar component central portion, is convex. 
     
     
       6. The ankle prosthesis of  claim 1 , wherein the first surface of the tibial component is convex and the first surface of the talar component is concave. 
     
     
       7. The ankle prosthesis of  claim 6 , wherein the first surface of the tibial component and the first surface of the talar component are defined by circle arcs. 
     
     
       8. A fixed-bearing ankle prosthesis comprising a tibial component and a talar component, wherein:
 the tibial component comprises a tibial attachment surface and a tibial articulating surface; 
 the talar component comprises a medial edge, a lateral edge, a talar attachment surface and a talar articulating surface, the talar articulating surface directly contacting the tibial articulating surface; 
 the tibial articulating surface comprises a medial concave condylar facet and a lateral concave condylar facet, each condylar facet having a radius of curvature in a medial-lateral plane that defines a respective circle arc, the facets separated from one another by a convex central portion; 
 the talar articulating surface comprises a medial convex condyle that underlies the medial condylar facet, and a lateral convex condyle that underlies the lateral condylar facet, the condyles separated from one another by a concave central portion that underlies the tibial convex central portion; 
 the medial condyle of the talar component has a first single radius of curvature in the medial-lateral plane that defines a convex circular arc cross-section continuously extending, in the medial-lateral plane, from the medial edge of the talar component to the concave central portion of the talar articulating surface; 
 the lateral condyle of the talar component has a second single radius of curvature in the medial-lateral plane that defines a convex circular arc cross-section continuously extending, in the medial-lateral plane, from the lateral edge of the talar component to the concave central portion of the talar component second surface; 
 the medial condyle radius of curvature is smaller than the medial condylar facet radius of curvature; and 
 the lateral condyle radius of curvature is smaller than the lateral condylar facet radius of curvature. 
 
     
     
       9. The ankle prosthesis of  claim 8 , wherein the talar condyle radii of curvature are between 92% and 96% of the corresponding tibial condylar facet radii of curvature. 
     
     
       10. The ankle prosthesis of  claim 8 , wherein the tibial attachment surface is convex and the talar attachment surface is concave. 
     
     
       11. The ankle prosthesis of  claim 10 , wherein the tibial attachment surface and the talar attachment surface are defined by circle arcs.